Method and apparatus for mode selection for high voltage integrated circuits

ABSTRACT

A method is disclosed to add functionality to a terminal of a high voltage integrated circuit without the penalty of additional high voltage circuitry. The benefit is that alternative modes of operation can be selected for testing, trimming parameters of the integrated circuit, or any other purpose without the cost of an additional terminal. In one embodiment, ordinary low voltage circuitry monitors the voltage on the terminal that normally is exposed to high voltage. The configuration of a simple voltage detector and an ordinary latch allows easy entry into the test and trimming mode when the integrated circuit is not in the intended application, but prohibits entry into the test and trimming mode when the integrated circuit operates in the intended application.

REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/119,373, filed May 12, 2008, now pending, which is a continuation ofU.S. application Ser. No. 11/527,803, filed Sep. 26, 2006, now U.S. Pat.No. 7,385,312, which is a continuation of U.S. application Ser. No.10/679,108, filed Oct. 3, 2003, now U.S. Pat. No. 7,157,813, entitled“Method and Apparatus for Mode Selection for High Voltage IntegratedCircuits.” U.S. application Ser. No. 11/527,803 and U.S. Pat. Nos.7,385,312 and 7,157,813 are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to integrated circuits, and morespecifically, the present invention relates to integrated circuits thatswitch high voltages in power converters.

2. Background Information

It is a common practice in the design of integrated circuits to includefunctions and modes of operation that are not used when the integratedcircuit is in its intended application. These alternative modes ofoperation may be used instead for a variety of purposes in theproduction of the integrated circuits and in the maintenance ofequipment that uses them. For example, it may be desirable to operatethe integrated circuit at special frequencies, voltages or currents thatreduce the time to test the device or that increase the accuracy andreliability of testing. The manufacturing process of some integratedcircuits includes an adjustment or trimming of internal parameters afterthe integrated circuit is assembled as part of the final test. Finaladjustment may be accomplished by selecting a special trimming mode ofthe integrated circuit. While in the trimming mode, parameters may beadjusted by appropriate manipulation of signals at the terminals of theintegrated circuit. The trimming mode may then be disabled after theadjustments are completed.

An alternative mode of operation could also be an alternative normalmode of operation, as distinguished from a test mode or a trimming mode.A normal mode of operation is one in which the integrated circuitoperates in its intended application. An alternative mode of operationthat is also a normal mode of operation might relate to the frequency ofa switching power supply. For example, one normal mode of operationcould use a fixed frequency whereas another normal mode of operationcould use a variable frequency. Some integrated circuits are fieldprogrammable, such that the user in each specific application may selectthe particular mode of operation.

The technology of most integrated circuits limits the voltage on theterminals to the maximum power supply voltage for the device, which istypically about 40 volts, but can vary depending on the manufacturingprocess and the feature size of the devices that comprise the integratedcircuit. The voltage is measured with respect to a ground referenceterminal that is usually a power supply terminal. The ground referenceterminal is typically at the most negative electrical potential of theintegrated circuit. In the subsequent discussion, such voltages that areusually less than about 40 volts are referred to as using ordinary lowvoltages. Terminals that can withstand a maximum voltage less than about40 volts are referred to as low voltage terminals. Terminals that canwithstand a maximum voltage substantially greater than about 40 voltsare referred to as high voltage terminals.

Some terminals of the integrated circuit may be limited to asubstantially lower voltage than the maximum power supply voltage. Inthe integrated circuits that are limited to ordinary low voltages,virtually any terminal of the device can be used to select alternativemodes of operation without difficulty because only low voltage circuitsare required to monitor the state of any terminal and to respond to anyvoltages that may be applied to the terminal.

Not all integrated circuits operate from low voltages. In the categoryof high voltage integrated circuits at least one terminal is exposed tohigh voltage in the intended application. These devices typicallyintegrate ordinary low voltage circuitry with a high voltage powersemiconductor. The high voltage terminal operates at voltages typicallygreater than 100 volts, which is substantially greater than the otherterminals will tolerate without damage. A common application for highvoltage integrated circuits is in switching power supplies. Forapplications in off-line alternating current (AC)-direct current (DC)power supplies, the voltage at the high voltage terminal can be in theneighborhood of 700 volts.

It will be recognized by one skilled in the art that the distinctionbetween high voltage terminals and low voltage terminals isfundamentally one of relative voltage and not absolute voltage. Forexample, an integrated circuit technology may use materials orgeometries such that ordinary low voltages are less than 1 volt, and anyvoltage greater than 10 volts is considered to be high voltage.

An objective in the design of integrated circuits is to realize thedesired functions at the lowest cost. Two factors that influence thecost of the integrated circuit are the amount of semiconductor materialand the number of terminals. Since high voltage devices are larger andtherefore use more semiconductor material than low voltage devices, itis advantageous to minimize the number of circuits that are exposed tohigh voltage in the integrated circuit. It is also advantageous to useeach terminal of the integrated circuit for as many functions aspossible to minimize the number of terminals.

SUMMARY OF THE INVENTION

Disclosed is a method to select alternative functional modes ofoperation of an integrated circuit through a terminal that can withstanda high maximum voltage. In one embodiment, an integrated circuitincludes a functional circuit coupled to a plurality of terminalsincluding first, second and third terminals of the integrated circuit.The first terminal is adapted to withstand a first maximum voltagerelative to the second terminal while the third terminal is adapted towithstand a second maximum voltage relative to the second terminal. Thesecond maximum voltage is substantially greater than the first maximumvoltage. The integrated circuit also includes a detector circuit coupledto detect a voltage at the third terminal. The detector circuit has afirst state when the voltage at the third terminal is less than a firstthreshold and the detector has a second state when the voltage on thethird terminal is greater than a second threshold. The integratedcircuit also includes a selector circuit coupled to the detector circuitand the functional circuit. The selector circuit is adapted to selectone of at least two distinct modes of operation for the functionalcircuit in response to the plurality of terminals. Additional featuresand benefits of the present invention will become apparent from thedetailed description, figures and claims set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention detailed illustrated by way of example and notlimitation in the accompanying Figures.

FIG. 1 is a block diagram of a high voltage integrated circuit of thetype that typically would be used in a switching power supply. It showsa high voltage power transistor and a controller.

FIG. 2 is a functional block diagram of the high voltage integratedcircuit of FIG. 1, showing internal elements of the controller thatrepresents a preferred embodiment of this invention.

DETAILED DESCRIPTION

An embodiment of a method for selecting alternative modes of operationin a high voltage integrated circuit is disclosed. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be apparent,however, to one having ordinary skill in the art that the specificdetail need not be employed to practice the present invention.Well-known methods related to the implementation have not been describedin detail in order to avoid obscuring the present invention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, the appearances of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments.

In the context of this disclosure, terminals of integrated circuits maybe either external or internal. External terminals couple to circuitryoutside the physical package of the integrated circuit, whereas internalterminals do not couple to circuits outside the package of theintegrated circuit. Terminals should be assumed to be external unlessotherwise stated.

A method for using a high voltage terminal of an integrated circuit toselect alternative functional modes of operation of the integratedcircuit in accordance with the teachings of the present invention willnow be described. Embodiments of the present invention involve methodsand apparatuses to select different configurations and functional modesof operation of the internal circuits through manipulation of voltagesat the terminals.

In one embodiment, the integrated circuit derives its internal powersupply from either the high voltage terminal or from a low voltageterminal, depending on the voltage present at each terminal. A voltagebuffer circuit limits the voltage from the high voltage terminal.Ordinary low voltage circuits detect the presence of high voltage on thehigh voltage terminal. An alternative mode of operation is selected whenvoltage is applied to the terminals with a particular sequence andmagnitude that cannot occur in the intended use of the integratedcircuit. Application of high voltage to the high voltage terminallatches the integrated circuit into its desired mode of operation.

In one embodiment of the present invention, a method is disclosed toselect a functional mode of operation of an integrated circuit by avoltage on a terminal that has the ability to withstand a high maximumvoltage in normal operation. The method uses ordinary low voltagecircuits to monitor the voltage on the high voltage terminal to add auseful function to the high voltage terminal without the burden andexpense of additional high voltage circuits.

In particular, a terminal that switches high voltage in normal operationis allowed to be a terminal that selects alternative modes of operation.The benefit in the use of a high voltage terminal for this purpose isgreatest for integrated circuits that have only a few terminals. Whereasit is relatively straightforward to encode multiple functions intointegrated circuits that have many low voltage terminals, the taskbecomes difficult when only a few terminals are available.

To illustrate, power integrated circuits with only three terminals arecommon in switching power supplies. In one embodiment, one of the threeterminals serves as the ground reference for the other two. Thus,integrated circuits with three terminals have only two terminalsavailable to perform all the required functions. One of the terminals isexposed to high voltage in normal operation. Therefore, the high voltageterminal must withstand a high maximum voltage. The method describedhere allows the use of the high voltage terminal to extend thefunctionality of the integrated circuit without the cost of anadditional terminal or the use of high voltage internal circuits.

In one embodiment, the integrated circuit contains a high voltagetransistor and a low voltage controller configured in a manner that issuitable for use in a switching power supply. FIG. 1 shows a typicalarrangement. In one embodiment, the integrated circuit is a switchedmode power supply controller that may be used to regulate the transferof energy from an input of a switching power supply to an output of theswitching power supply through an energy transfer element. Inside theenvelope of integrated circuit 100 are a high voltage power transistor101 and a controller 102. In one embodiment, the transistor is a fieldeffect device with its drain coupled to the high voltage terminal 103and its source coupled to a ground reference terminal 104. Controller102 is coupled to terminals 103 and 104 by internal connections.

In one embodiment, the controller 102 is also coupled to a terminal 105that receives signals from external circuits and internal circuits tomaintain desired operation of the integrated circuit. In one embodimentthe terminal 105 is a control terminal, a power supply terminal as wellas a functional terminal. For purposes of this disclosure, a controlterminal is one that regulates a switching power supply. A power supplyterminal is one that is coupled to the voltage and current necessary tooperate the internal circuits. A functional terminal is one thatperforms any other desired operation on the integrated circuit. Anynumber of additional terminals 106 may be present as required fordesired functions.

In one embodiment, the integrated circuit 100 of FIG. 1 includes theelements illustrated in FIG. 2. As shown in the embodiment depicted inFIG. 2, controller 200 is coupled to the high voltage terminal 103 byinternal connection 201, and to the ground reference terminal 104 byinternal connection 214. In one embodiment, controller 200 is includedin a switching power supply controller that may be used to regulate thetransfer of energy from an input of a switching power supply to anoutput of the switching power supply through an energy transfer element.In the following description, all voltages should be assumed to berelative to the ground reference terminal 104 or internal connection 214unless otherwise stated.

In one embodiment, a high voltage buffer circuit 204 is adapted toprovide internal voltages 203 and 205, which are not allowed to exceedlimits that are safe for the low voltage devices in the controller 200.The internal voltages are typically is less than 40 volts, as inordinary low voltage integrated circuits. In one embodiment, theinternal voltage 203 is limited to 36 volts, and the internal voltage205 is limited to 15 volts. One skilled in the art will be familiar withthe design of high voltage buffer circuits. A Zener diode, a junctionfield effect transistor (JFET) resistor, and a voltage-controlledcurrent source are some examples of known circuits that could besuitable for high voltage buffer circuits in particular applications inaccordance with the teachings of the present invention.

In one embodiment, an internal voltage regulator circuit 202 receivesthe internal voltage 203 and delivers a regulated voltage 206 that isless than the buffered higher internal voltage 203. One skilled in theart will be familiar with the design of suitable voltage regulatorcircuits. The regulated voltage 206 is typically about 5 volts. In oneembodiment the regulated voltage is 5.8 volts.

As shown in the depicted embodiment, the voltage regulator circuit 202is also coupled to terminal 207 that in one embodiment is a controlterminal, a power supply terminal and a functional terminal. In oneembodiment, terminal 207 is not coupled to any circuitry external to theintegrated circuit. In such an embodiment, the integrated circuit wouldhave only two external terminals, which are terminals 103 and 104 in theembodiments illustrated in FIGS. 1 and 2. In one embodiment, voltageregulator 202 can provide regulated voltage 206 from either the internalvoltage 203 or from a voltage at terminal 207 so long as either internalvoltage 203 or the voltage at terminal 207 is sufficiently greater thanthe regulated voltage 206.

A functional circuit 208 performs all other functions that are notexplicit in the FIG. 2. In one embodiment, the gate of the powertransistor is driven by a signal 213 from functional circuit 208. Adriver circuit to generate signal 213 is included in functional circuit208.

In one embodiment, functional circuit 208 monitors the regulated voltage206. When the regulated voltage 206 is high enough for proper operation,an internal signal 212, which is labeled “V_(DD) GOOD” in FIG. 2,provided by functional circuit 208 goes to the logic high state. Theinternal signal 212 is at the logic low state when the regulated voltage206 is too low for the circuits to operate properly. A voltage monitorcircuit to monitor the regulated voltage 206 is included in functionalcircuit 208.

In one embodiment, a mode management circuit that is included infunctional circuit 208 receives a mode select signal 209 that selects analternative mode of operation for controller 200. For example, when themode select signal 209 is at logic low and controller 200 is thereforein the alternative mode of operation, a signal at terminal 207 or any ofthe other functional terminals can change the behavior or theconfiguration of the functional circuit 208. The changes can be eithertemporary or permanent. In one embodiment, logic low on mode selectsignal 209 causes the integrated circuit to enter the alternative modeof operation that allows testing and trimming. A logic high on modeselect signal 209 causes the controller 200 to enter the normal mode ofoperation and leave the alternative mode of operation that allowstesting and trimming. It is appreciated that although the alternativemode of operation is being described herein for example purposes as amode of operation for testing and trimming, other modes of operation maybe accomplished with the alternative mode of operation, including othernormal modes of operation in accordance with the teachings of thepresent invention.

In one embodiment, the alternative mode of operation that allows testingand trimming is prohibited when the integrated circuit is used in itsintended application during the normal mode of operation. In oneembodiment, in the intended application, voltage is applied to the drainterminal 103 at internal connection 201 before there is voltage on anyother terminal. The presence of voltage on the drain terminal 103activates the high voltage buffer 204 so that voltage appears at itsoutput of internal voltage 205 that is coupled to a detector circuit211. In one embodiment, the detector circuit 211 includes an ordinarycomplementary metal oxide semiconductor (CMOS) inverter, as shown inFIG. 2, which will be familiar to one skilled in the art.

As illustrated in the embodiment depicted in FIG. 2, a selector circuit210 generates the mode select signal 209 in response to the inputreceived from the output of detector circuit 211 as well as the internalsignal 212 received from functional circuit 208. In yet anotherembodiment, it is appreciated that selector circuit 210 may beresponsive to other influences such as for example signals present onother internal or external terminals including for example terminal 207or the like. Thus, since the output of detector circuit 211 and theinternal signal 212 provided by functional circuit 208 are responsive toconditions at for example terminals 103 and 104, and since selectorcircuit 210 may also be responsive to other terminals such as forexample terminal 207, selector circuit 210 correspondingly generatesmode select signal 209 in response to for example terminals 103, 104and/or 207 in accordance with the teachings of the present invention.

In one embodiment, when the internal voltage 205 at the input to thedetector circuit 211 is greater than a threshold of for example 2.9volts, the detector circuit 211 causes a selector circuit 210 to bringthe mode select signal 209 from a logic low to a logic high. The modeselect signal 209 output from the selector circuit 210 is allowed toreturn to its original state when the signal 212 goes to logic low. Thesignal 212 goes to logic low when the regulated voltage 206 is too lowfor all the circuits to operate properly.

In one embodiment, the configuration of the selector circuit 210includes ordinary latch circuitry, as shown in FIG. 2, which will befamiliar to one skilled in the art, which assures that the integratedcircuit in its intended application can never inadvertently enter thealternative mode that allows testing and trimming when controller 200 isoperating in normal mode in its intended application. For instance, thelatch of selector circuit 210 holds the mode select signal 209 at logichigh even when the internal voltage 205 from the high voltage bufferdoes not stay above the threshold of for example 2.9 volts, as wouldoccur in the normal operation of a switching power supply.

In one embodiment, the alternative mode for testing and trimming isenabled only through a simple sequence that does not occur during thenormal mode of operation in the intended application. For example, inone embodiment, to enter the test and trimming mode, all terminals 103,104 and 207, are initially set to zero volts. Terminal 207 is raised toapproximately 5.8 volts while the voltage at the drain terminal 103 atinternal connection 201 remains low enough to keep the internal voltage205 at the input to the detector circuit 211 below the threshold ofapproximately 2.9 volts. As the regulated voltage 206 rises, theselector circuit 210 holds the mode select signal 209 at logic low toallow the alternative mode for test and trimming. Application of enoughvoltage on the drain terminal 103 at internal connection 201 to raisethe internal voltage 205 above the threshold of for exampleapproximately 2.9 volts will latch the mode select signal 209 at logichigh to leave the test and trimming mode.

In one embodiment, the threshold of the detector circuit 211 may bevariable or adjustable in response to the signals at a plurality of lowvoltage terminals. In another embodiment, the threshold of the detectorcircuit 211 has hysteresis, such that the threshold changes between afirst threshold and a second threshold, depending on the voltage at theinput to the detector circuit 211. It is appreciated that the design ofcircuits with thresholds that have hysteresis will be familiar to oneskilled in the art.

In the foregoing detailed description, the method and apparatus of thepresent invention have been described with reference to a specificexemplary embodiment thereof. It will, however, be evident that variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the present invention. The presentspecification and figures are accordingly to be regarded as illustrativerather than restrictive.

1. A method of selecting modes of operation of a power supply controlintegrated circuit, comprising: setting a high voltage terminal, areference terminal, and a third terminal of the power supply controlintegrated circuit to a first voltage; buffering the voltage at the highvoltage terminal to provide an internal voltage to low voltage circuitryof the power supply control integrated circuit, wherein the internalvoltage is representative of the voltage at the high voltage terminal,wherein the low voltage circuitry is adapted to withstand a firstmaximum voltage relative to the reference terminal, wherein the highvoltage terminal is adapted to withstand a second maximum voltagerelative to the reference terminal, wherein the second maximum voltageis substantially greater than the first maximum voltage; raising thevoltage at the third terminal to a second voltage; and enabling analternative mode of operation of the power supply control integratedcircuit with the low voltage circuitry in response to detecting that theinternal voltage is below a first threshold voltage.
 2. The method ofclaim 1, wherein the first voltage is zero volts.
 3. The method of claim1, wherein the second voltage is approximately 5.8 volts.
 4. The methodof claim 1, further comprising: raising the voltage at high voltageterminal; and disabling the alternative mode of operation and enabling anormal mode of operation of the power supply control integrated circuitwith the low voltage circuitry if the internal voltage is above a secondthreshold voltage.
 5. The method of claim 4, further comprisingswitching a power switch during the normal mode of operation of thepower supply control integrated circuit, wherein the power switch iscoupled between the high voltage terminal and the reference terminal ofthe power supply control integrated circuit.
 6. The method of claim 4,wherein the first threshold voltage is equal to the second thresholdvoltage.
 7. The method of claim 4, wherein the first and secondthreshold voltages are equal to approximately 2.9 volts.
 8. The methodof claim 4, further comprising latching the power supply controlintegrated circuit to the normal mode of operation to assure that thepower supply control integrated circuit does not enter the alternativemode of operation during an intended use of the power supply controlintegrated circuit.
 9. The method of claim 1, wherein enabling thealternative mode of operation comprises setting the power supply controlintegrated circuit to a testing mode of operation that is different froma normal mode of operation.
 10. The method of claim 1, wherein settingthe alternative mode of operation comprises setting the power supplycontrol integrated circuit to a trimming mode that is different from anormal mode of operation.
 11. The method of claim 1, wherein theinternal voltage is a first internal voltage, the method furthercomprising: buffering the voltage at the high voltage terminal toprovide the first internal voltage and a second internal voltage to thelow voltage circuitry of the power supply control integrated circuit;and regulating the second internal voltage with a voltage regulatorcircuit to provide the low voltage circuitry with a regulated voltage.12. The method of claim 11, further comprising: monitoring the regulatedvoltage; and generating an internal signal, having a logic high and alogic low state, indicating whether the regulated voltage is high enoughfor proper operation of at least some of the low voltage circuitry. 13.The method of claim 11, further comprising regulating a voltage receivedat the third terminal of the power supply control integrated circuit toprovide the low voltage circuitry with the regulated voltage, whereinthe third terminal is adapted to withstand the first maximum voltagerelative to the reference terminal.
 14. The method of claim 13, whereinregulating the second internal voltage and regulating the voltagereceived at the third terminal comprises: regulating the second internalvoltage to provide the regulated voltage if the voltage received at thethird terminal is less than the regulated voltage; and regulating thevoltage received at the third terminal to provide the regulated voltageif the second internal voltage is less than the regulated voltage. 15.The method of claim 1, further comprising adjusting the first thresholdvoltage in response to a signal received at the third terminal, whereinthe third terminal is adapted to withstand the first maximum voltagerelative to the reference terminal.